1. Technical Field
The present disclosure relates generally to a method of manufacturing a liquid dispenser head, the liquid dispenser head, a liquid dispensing unit having the liquid dispenser head, and an image forming apparatus having the liquid dispenser head.
2. Description of the Background Art
In general, an image forming apparatus is available as a printer, a facsimile machine, a copier, a plotter, or a multi-functional apparatus having multiple functions thereof. Such image forming apparatus may include a liquid dispensing unit having a liquid dispensing head (or a recording head) for dispensing droplets of recording liquid onto a recording sheet to form an image on the recording sheet.
Such sheet includes, but is not limited to, a medium made of material such as paper, string, fiber, cloth, leather, metal, plastic, glass, timber, and ceramic, for example. Further, the term “image formation” used herein refers to providing, recording, printing, or imaging an image, a letter, a figure, or a pattern to a sheet. Moreover, the term “liquid” used herein is not limited to recording liquid or ink but includes anything discharged in fluid form. Hereinafter, the recording liquid is referred to as ink for simplicity of description.
Furthermore, a liquid dispensing unit having a liquid dispenser head can be used in any application area, including, but not limited to, forming an image on a sheet, dispensing liquid for specific purposes (e.g., fabrication of semiconductor), and the like.
Such liquid dispensing unit or image forming apparatus have found industrial applications in such fields as cloth-printing apparatuses and metal wiring devices, while commercial demand for better image quality and faster printing speed continues to grow.
In view of such demand for better image quality, nozzle density, or a number of nozzles per unit area of the liquid dispenser head, continues to increase, narrowing spacing between pressure chambers of a recording head and increasing an energy frequency, or number of vibrations applied to the recording head.
Further, in view of such demand for faster printing speed, a line printer having page-wide arrays (PWA) of recording head has been developed. The main advantage of such PWA head is that it has a length sufficient to print a single line image on a recording medium with a single liquid discharge. However, a drawback of such PWA head is that its manufacture requires consistently high precision to very narrow tolerances.
In general, a recording head or liquid dispenser head includes a nozzle, a liquid chamber that communicates with the nozzle, and a pressure generator to generate pressure for discharging liquid droplets from the nozzle.
Such recording head may use known methods for discharging liquid droplets, such as a thermal method, a piezoelectric method, and an electrostatic method. In the thermal method, an electricity-heat conversion element such as a heating resistor is used to cause a film boiling of liquid. In the piezoelectric method, an electricity-mechanical energy conversion element such as a piezoelectric element is used. In the electrostatic method, an electrostatic actuator, which generates electrostatic force, is used.
A liquid dispenser head employing a piezoelectric element may have an elastically deformable vibration plate, with a protruded portion (or convex portion, or island portion) provided on the vibration plate in a direction extending in a longitudinal direction of the liquid chamber, in which a displacement energy of the piezoelectric element is transmitted to the vibration plate via the protruded portion.
Such protruded portion is provided on the vibration plate to effectively deform a wall face of the liquid chamber and to suppress interference between adjoining liquid chambers.
In general, the vibration plate is made of polymer film bonded to a thin metal plate. For example, the polymer film is bonded to the thin metal plate with an adhesive agent and the thin metal plate is etched to form the protruded portion (or island portion), in which an area other than the island portion may be coated with the adhesive agent.
Alternatively, a thermosetting resin such as thermosetting polyimide may be directly applied to a SUS (stainless steel) plate to form the vibration plate.
Although such polymer film product or thin metal plate product may have a variable thickness, such thickness in variation of product may similarly appear when manufacturing products having different sizes. For example, a thickness in variation of a polymer film having larger area and a polymer film having smaller area may have a similar trend, as may a thickness variation of a thin metal plate having larger area and a thin metal plate having smaller area.
Accordingly, even if the liquid dispenser head is enlarged or lengthened, the thickness (or height) of the protruded portion of the vibration plate can be controlled to within a given thickness variation.
A different problem arises, however, in that an etching with etchant is conducted on the thin metal plate of the vibration plate, which is prepared by bonding the polymer film to the thin metal plate with an adhesive agent as described above. Consequently, the adhesive agent may come into contact with the etchant during the etching, by which the adhesive layer may be eroded or partially degraded by the etchant. Such erosion or degeneration of the adhesive layer may cause variation in thickness of the vibration plate, which may result in unacceptable variation in vibration performance of the vibration plate.
Furthermore, variation in thickness of the polymer film and variation in thickness of the adhesive layer may cause unacceptable variation in vibration performance of the vibration plate.
If a resin layer such as a polyimide is directly applied to and formed on the thin metal plate (e.g., SUS plate) without using an adhesive layer, such variation in thickness of the adhesive layer is, of course, no longer an issue for liquid dispenser head manufacture.
Such resin material (e.g., polyimide) must be heated to a higher temperature for imidization and cooled to room temperature to form a vibration plate having a resin layer formed directly on a metal plate, wherein such method is called a varnish method.
After forming the resin layer on the metal plate, some portion of the metal plate is removed by etching. When such etching is conducted, a portion of the resin layer corresponding to a removed portion of the metal plate (i.e., etched portion of the metal plate) may wrinkle.
More specifically, the vibration plate has a vibrating portion made of a resin layer and a protruded portion (or island portion) made of a metal layer. Such protruded portion of the vibration plate is bonded to a piezoelectric element.
Because some portion of the metal layer is removed by etching to form the protruded portion, some portion of the resin layer, which corresponds to the removed portion of the metal layer, is no longer bonded to the metal layer. Such portion of the resin layer may be termed a “resin only portion,” and wrinkles are more likely to appear in such resin only portion area of the resin layer.
If such wrinkles do appear in the resin layer of the vibration plate, displacement energy of the piezoelectric element may not be effectively transmitted to the liquid chamber, thus degrading droplet discharge performance or creating unacceptable variation in the droplet discharge performance of each liquid chamber (or nozzle).